Mcux Ethernet driver does not detect carrier anymore (it's alway on)

[tbursztyka]

Describe the bug
Mcux Ethernet driver used to be able to detect carrier state, but something somewhere has changed and it thinks the carrier is always on now.

To Reproduce
Do not plug the Ethernet cable to your device
Use samples/net/sockets/echo_client

1. mkdir build; cd build
2. Change the prj.conf so it becomes:

#CONFIG_NET_CONFIG_MY_IPV6_ADDR="2001:db8::2"
#CONFIG_NET_CONFIG_PEER_IPV6_ADDR="2001:db8::1"
#CONFIG_NET_CONFIG_MY_IPV4_ADDR="192.0.2.2"
#CONFIG_NET_CONFIG_PEER_IPV4_ADDR="192.0.2.1"
CONFIG_NET_DHCPV4=y
CONFIG_NET_L2_ETHERNET_MGMT=y
CONFIG_NET_MGMT_EVENT_LOG_LEVEL_DBG=y
CONFIG_NET_DHCPV4_LOG_LEVEL_DBG=y

3. cmake -DBOARD=board\frdm_k64f
4. make
5. Dhcp starts right away to send discover
6. Plug the Ethernet cable: no changes. Eventually the discover timeout will restart and dhcp will be successful but that's the wrong behavior: it should receive a if_up net_mgmt event then starts dhcp discover.

Expected behavior
Carrier on/off (and thus net if up/down state) should be detected

Impact
Unable to test properly code that rely on carrier off/on and net if up/down events on that device.

[MaureenHelm]

@agansari can you take a look at this?

[ioannisg]

@tbursztyka pls, try the patch in #17847 and report if this fixes the bug :)

[tbursztyka]

I'll try to find some time next week, too busy atm.